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Many digital cameras display an exposure scale when you use exposure compensation.

Click to explore how exposure controls how light or dark an image is.

Click to explore exposure compensation.

Pressing the shutter button halfway down locks exposure (and focus) and pressing it all the way down takes the picture.

Click to explore exposure lock.

A camera's exposure system can't think. Regardless of the scene, its subject matter, color, brightness, or composition, the system does only one thing—it measures the average brightness, or how light or dark the overall scene is. The system then calculates and sets the aperture and the shutter speed to render this average level of brightness as "middle gray" in the photograph. Most of the time this works very well because most scenes have an overall brightness that averages out to middle gray. But some scenes don't and that's when autoexposure will lead you astray. That's why most digital cameras provide ways to override the exposure system so you get the exposure you want. The most common choices are exposure compensation and exposure lock.

Exposure Compensation

You can't make an image lighter or darker by changing the shutter speed or aperture in any mode but manual. In other modes when you change one of the settings, the other changes automatically to keep the exposure constant. Exposure compensation is the feature you use to capture an image that's lighter or darker than one the camera would produce automatically. To lighten a picture, you increase the exposure; to darken it, you decrease the exposure. The amount you increase or decrease the exposure is specified in stops. If you select a + value, the image will be brighter. If you select a – value it will be darker. It's easy to use exposure compensation because most cameras display a scale to guide you and you can preview the effects of your changes on the monitor. You can also check an image in review or playback mode and even examine its histogram on many cameras.

When you adjust exposure compensation you can do so in full stops and sometimes even finer increments—usually one-third or one-half stops. On many cameras you will see a scale displayed when you use this command. The "0" indicates the exposure suggested by the camera. As you adjust the exposure toward the plus (+) side of the scale the image gets lighter. As you adjust it toward the minus (-) side it gets darker. Here you see the results as it's adjusted from +2 (left) to -2 (right). The effect of the changes on the image are dramatic.

SLOWING DOWN

The Fuji W1/W3's slowest shutter speed is normally ½ second. However, these cameras have a Night Tripod mode that let's you use slower shutter speeds. This lets you get better exposures in dim light but you should expect a great deal of noise in your images.

AutoExposure lock (AE Lock)

You can adjust exposures with a procedure called autoexposure lock (AE Lock). To do so you point the camera at the part of the scene on which you want to base the exposure and press the shutter button halfway down. The camera then calculates the exposure (and focus) and locks them in. While continuing to hold down the shutter button, you recompose and shoot the picture using the locked in settings.

To see what an impact this can have, point your camera so the sky occupies at least three-quarters of the frame and press the shutter button halfway down to lock exposure. Recompose the image so the sky occupies only half of it and take the picture. Now do exactly the same but this time have the foreground occupy at least three-quarters of the frame before you lock exposure. Compare the two images and you will find that in the first the sky is properly exposed but the foreground is too dark. In the second, the foreground is properly exposed but the sky is too light. As you get more experienced with this technique you learn to recognize parts of the scene that will give you the exposure you are looking for.

Here Emily looks through a window in a museum diorama while I photograph her through another window.